This invention relates to an apparatus for measuring light scattering. More particularly, this invention measures near direct-forward scattering function of light in water for underwater imaging.
Currently there is renewed interest in developing electro-optic sensors for underwater imaging used in the detection, classification, and identification of a number of submerged objects, such as mines. The performance of these sensors is strongly influenced by the characteristics of the water in which they are operated. For acceptable imaging one of the most influential environmental parameters which affects the performance is scattering. In particular, the parameter, or function of near-direct forward scattering that is attributed to the water medium and dissolved and particulate matter in the water medium dominates the ability to resolve fine details of images.
Historically, this scattering function has been difficult to measure, and no available sensors are known to accurately perform this measurement. In fact, direct measurement of the scattering phase function has not been attempted often. The report, “Volume Scattering Functions for Selected Ocean Waters” by Scripps Institution of Oceanography for Naval Air Development Center, October 1972, National Technical Information Service AD-753 474, is the only known published account of direct measurements available. The device of the Scripps report used a movable detector that could be positioned over essentially the full arc from the direction the beam was emitted to the direction the beam was directly reflected (0-180 degrees relative to the direction of the emitted beam). The arc the movable detector traveled was large, making it acceptable for effective real-time scientific measurements; however, the device was not suitable for general use at work sites in the ocean.
Indirect measurements of other phenomena in the water have been made on occasion in the form of Modulation Transfer Functions (MTFs) and Point Spread Functions (PSFs). But these measurements are not directly relatable to the underlying scattering function, as they provide a measurement of integrated effects from which the scattering function cannot be extracted.
Thus, in accordance with this inventive concept, a need has been recognized in the state of the art for a detector apparatus deployable in the ocean to measure near-direct forward scattering of ambient water.